This invention relates to circuits for processing colour television signals in the PAL or N.T.S.C. system.
It is frequently desired to separate a composite PAL colour television signal into its luminance and chrominance components. The simplest methods involve only band-pass filters, but these are crude, introduce considerable cross-colour, and largely negate many of the advantages of the PAL system. One improved method is described in cognate British Patent Applications Nos. 22567/77 and 51668/77 (publised as German Offenlegungsschrift 28 22 668), which uses delays of one line plus or minus a quarter cycle of subcarrier. Another improved method is described in British Pat. No. 1,511,230 and developed in Brit. Pat. No. 1,524,749 and Application No. 15811/77. However these improved methods are, at least in general, inapplicable to processing systems which use line-locked sampling and furthermore require relatively complicated circuitry.
This invention enables the provision of a processing system in which line-locked sampling can be used, and which is of relatively uncomplicated construction. At the least, the invention provides a useful alternative to the previously known systems. Apart from separating a composite PAL signal into its luminance and chrominance components, the system may also be useful in filtering the luminance component of a PAL signal to remove componenets likely to cause cross-colour, or in filtering a combination of the luminance and chrominance components in a PAL coder.